Probably because the part time job doesn't take tax off as if it is your second job, but as if it is your only job.

@jay931 The amount of tax due depends on your income.  The more you earn, the higher your calculated income tax will be. This is called a progressive (or graduated) tax system. 

Income tax brackets are ranges of income on which a set rate of tax is applied.

• Canadian taxpayers pay income tax to the federal government as well as to the government of the province/territory where they reside.
• Credits and deductions are 2 common ways of reducing your taxes owing and/or increasing your tax refund.

Canada Taxes 2024: Federal Tax Brackets, Rates and Credits

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